TL;DR version for best results in story mode:
Place a Refinery for every 200$ worth in a crystal. In practice this usually results in placing four refineries on every single crystal since they usually are of value 1000$ and above. Only place Reprocessors in such a manner that will allow them to improve the processing of at least 2500$ worth of crystal. This means that refineries augmented by a reprocessor should cumutively process at least 2500$ either from a single large source or several smaller crystals given smart placement.The full discussion:
There are two opposing considerations - maximum cost-effective extractable value from cystals and staying alive (cashflow).The absolute maximum value that can be extracted from a crystal is its base value (revealed on mouseover) multiplied by 1.8 (1.9 if Extraction Calibration is researched). This is achieved by placing a single Refinery with four Reprocessors on a 3000$+ crystal and having the level last the ~2.5+ minutes it will be required to mine the crystal.
The math for this is:
- A reprocessor costs 750$ upfront and is recycled/sold for 40%, regaining 300$. Building one sinks 450$
- A reprocessor adds 20% to connected Refineries' generated value, up to 80% (revealed experimentally)
- To break even a Reprocessor has to process 2250$ worth i.e. 225 instances of processing (450$=20%, 100%=2250$)
- A suite of 1 Refinery, 1 Collector and 4 Reprocessors costs 3750$
- Given the time to mine the crystal completely, such a setup will generate 5400$, breaking even (covering the 60% sell loss) at 1250$ processed
- Adding 1500$ - the 40% of selling the suite -, the operation turnover amounts to 6900$, a 84% profit
Cashflow is best maintained by placing four refineries as quickly as possible on all available crystals and researching Extraction Tuning. One might also consider placing a collector that covers four refineries or more (possible on adjacent crystals). See my preferred YinYang pattern for space-effective placement.
Finally, you absolutely want to drag the levels out as long as possible to mine all crystal, here is why. Crystal scavenging is at 10% (15% in endless). You lose 90% of their value! For a refinery to make you a profit it needs to process at least 160$ worth. So the only circumstance where it is profitable not to mine a crystal is when a crystal contains 150$ worth or less (I imagine one will only get such a crystal if Titans had laid waste to previous mining operation).
I recommend leaving some amount of concrete barricades for the end of the level for slowing down a couple of the last weakling titans and giving your refineries extra time for mining. A barricade is 10$ a pop and given a couple of operational refineries they pat for themselves if they slow the Titans even for a couple seconds.
Furthermore, there are some peculiar differences in recycling behavior in story mode and endless. In story, everything sellable is sold at the end of the level. In endless, refineries are scrapped for 80% their worth, blasters are left unsold. I only bothered to test first couple of levels and I have no idea what recycling behavior is applied to addons and advanced weaponry beyond blasters, but as far as I can surmise for best results one should sell all non-refinery buildings at the end of an endless level (maybe someone can test whether refinery addons are scrapped or left unsold as well in endless).
That will be all, thank you.
